Metalworking fluids long have been used in the cutting and abrasive working of metals. In such operations, including cutting, milling, drilling, and grinding, the purpose of the fluid is to lubricate, cool, and to remove fines, chips and other particulate waste from the working environment. In addition to cooling and lubricating, these fluids also can serve to prevent welding between a work piece and tool and can prevent excessively rapid tool wear. See Jean C. Childers, The Chemistry of Metafworking Fluids, in METAL-WORKING LUBRICANTS (Jerry P. Byers ed., 1994).
A fluid ideally suited as a coolant or lubricant for cutting and abrasive working of metals and ceramic materials must have a high degree of lubricity. It must also, however, possess the added advantage of being an efficient cooling medium that is non-persistent in the environment, is non-corrosive (i.e., is chemically inert), and does not leave a residue on either the working piece or the tool upon which it is used.
Today's state of the art working fluids fall generally into two basic categories. A first class comprises oils and other organic chemicals that are derived principally from petroleum, animal, or plant substances. Such oils commonly are used either straight (i.e., without dilution with water) or are compounded with various polar or chemically active additives (e.g., sulfurized, chlorinated, or phosphated additives). They also are commonly solubilized to form oil-in-water emulsions. Widely used oils and oil-based substances include the following general classes of compounds: saturated and unsaturated aliphatic hydrocarbons such as n-decane, dodecane, turpentine oil, and pine oil; naphthalene hydrocarbons; polyoxyalkylenes such as polyethylene glycol; and aromatic hydrocarbons such as cymene. While these oils are widely available and are relatively inexpensive, their utility is significantly limited; because they are most often nonvolatile under the working conditions of a metalworking operation, they leave residues on tools and working pieces, requiring additional processing at significant cost for residue removal.
A second class of working fluids for the cutting and abrasive working of metals includes chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and perfluorocarbons (PFCs). Of these three groups of fluids, CFCs are the most useful and are historically the most widely employed. See, e.g., U.S. Pat. No. 3,129,182 (McLean). Typically used CFCs include trichloromonofluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, 1,1,2,2-tetrachlorodifluoroethane, tetrachloromonofluoroethane, and trichlorodifluoroethane. The most useful fluids of this second general class of metal working fluids (CFCs & HCFCs) possess more of the characteristics sought in a cooling fluid, and while they were initially believed to be environmentally benign, they are now known to be damaging to the environment. CFCs and HCFCs are linked to ozone depletion (see, e.g., P. S. Zurer, Looming Ban on Production of CFCs, Halons Spurs Switch to Substitutes, CHEM. & ENG'G NEWS, Nov. 15, 1993, at 12). PFCs tend to persist in the environment (i.e., they are not chemically altered or degraded under ambient environmental conditions).